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Any court action has the possibility of delaying the referendum, which is due to be staged on September 18th of this year, although Mr O'Neill wishes it to be fast-tracked to the Supreme Court.

In excess of 2,700 signatures have been collected so far in favour of a legal challenge. Famous supporters of the move include Kenny Logan, husband of TV presenter Gabby Logan, and Alex McLeish, a former football manager for Scotland, who now live in England.

The legal action will also be costly, with donations towards the £100,000 it will take to complete being sought.

If Scotland does become independent then its status within the EU is likely to be unknown for a brief period at least.

This could be difficult for expat Scots as they could lose their rights to free healthcare and other benefits in the EU, while the situation is being clarified. It could also affect their right to work.

So despite not being granted a vote, expats are likely to be directly impacted by the decision that is made by their fellow citizens.

The Scottish government has rebuffed claims by Mr O'Neill that there is a legitimate legal case to challenge the decision to exclude expat voters.

A spokeswoman told the Scotsman: "The Edinburgh Agreement confirmed that the franchise for the referendum was for the Scottish Parliament to determine, and it is widely accepted that the ­Edinburgh Agreement has put the referendum beyond effective legal challenge."